This application claims priority to an application entitled xe2x80x9cApparatus and Method for Measuring Bit Error Rate in an OFDM Communication Systemxe2x80x9d filed in the Korean Industrial Property Office on Jan. 28, 2000 and assigned Ser. No. 2000-4310, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to an orthogonal frequency division multiplexing (OFDM) communication system, and in particular, to an apparatus and method for measuring a bit error rate (BER) using a pilot sub-channel in an OFDM communication system.
2. Description of the Related Art
The OFDM is a form of multi-carrier modulation technique. In OFDM each carrier is orthogonal to the other carriers. This modulation technique uses parallel data and frequency division multiplexing (FDM) with overlapping sub-channels to avoid the use of high-speed equalization, to combat impulsive noise and multi-path distortion, as well as to fully use the available bandwidth. A comparison between the OFDM system and a single-carrier system will be made, for the same transmission bandwidth and the same transfer rate. When the transmission data is dispersedly transmitted with N carriers, the duration of one transmission symbol for the OFDM system becomes N times longer than that of the single-carrier system. Therefore, the OFDM system can prevent degradation of the transmission characteristics by simply adding a bit guard interval on a time domain, even if there exists a multi-path interference. In addition, the data is dispersedly transmitted over the entire transmission band. Therefore, it is possible to effectively improve the characteristics by means of an interleaver and an error correction code, even though there exists an interference signal at a specific frequency band, since its influence is limited to only part of the data.
A conventional technique for measuring such a bit error rate uses a SNORE (Signal-to-Noise Ratio Estimation) algorithm. The SNORE algorithm calculates a bit error rate by using signal power and noise power. Specifically, the SNORE algorithm estimates a signal-to-noise ratio (SNR) by calculating average and variance of a received signal, and then calculates the bit error rate according to the estimated SNR. The SNR can be estimated using Equations (1) and (2) below.                                           E            b            xe2x80x3                                N            o                          =                                            SN              xe2x80x3                        ⁢            R                    -                                                    (                                  μ                  xe2x80x3                                )                            2                                      2              ⁢                              σ                xe2x80x32                                                                        (        1        )                                          μ          xe2x80x3                =                              1            n                    ⁢                                    ∑                              i                =                0                            n                        ⁢                          "LeftBracketingBar"                              X                i                            "RightBracketingBar"                                                          (        2        )            
where xcexcxe2x80x3 is an average value of samples, "sgr"xe2x80x3 is a particular sample, n is the total number of samples, and X is a received signal.
It is possible to calculate the bit error rate from a BER mapping table using the SNR value estimated in accordance with Equations (1) and (2). Since the SNORE algorithm using the SNR must calculate the average and variance of the received signal, it requires complicated calculations and additional circuitry. Further, since the variance of the estimated SNR is large, it is not possible to calculate an accurate BER.
It is, therefore, an object of the present invention to provide an apparatus and method for measuring a bit error rate using a pilot sub-channel in the data OFDM symbol.
It is another object of the present invention to provide a method for correctly measuring a bit error rate by comparing a demodulated received pilot pattern with a reference pilot pattern using a pilot sub-channel in an OFDM communication system.
To achieve the above and other objects, there is provided an apparatus for measuring a bit error rate (BER) in an OFDM communication system. A transmission device includes a pilot pattern inserter for inserting a first reference pilot pattern in subchannels of data OFDM symbol, and an OFDM modulator for OFDM-modulating the reference pilot pattern-inserted transmission data. A receiver includes a pilot pattern detector for OFDM-demodulating a data symbol received in a frame unit and detecting only a pilot pattern, and a BER operator for comparing the demodulated pilot pattern with a second reference pilot pattern, detecting and accumulating the number of pilot errors, and measuring a bit error rate by dividing the accumulated number of the pilot errors by the number of total received pilot patterns.
A method for measuring a bit error rate in an OFDM communication system according to the present invention comprises: upon receipt of transmission data, inserting a first reference pilot pattern in a data symbol, OFDM-modulating reference pilot pattern-inserted data symbol, and transmitting the modulated data symbol in a frame unit; demodulating the data symbol received in the frame unit, detecting a pilot pattern from the demodulated data symbol, and calculating the number of the total received pilots by accumulating the detected demodulated pilot pattern; comparing the detected demodulated pilot pattern with a second reference pilot pattern to detect pilot errors, and accumulating the number of the detected pilot errors; and measuring a bit error rate by dividing the accumulated number of the pilot errors by the number of the total received pilot patterns.